The present invention refers to a component defining one of a blade and a vane for a rotary machine having a rotor which is rotatable about an axis, said component comprising an inner space, forming a passage for a cooling fluid and limited by first and second walls facing each other, and at least first ribs, projecting form said first wall and extending essentially in parallel to each other to form first channels for said fluid from a leading inlet part of the inner space to a trailing outlet part of the inner space.
Although, the present invention is applicable to rotor blades as well as stator guide vanes, it is merely referred to blades in the following description for the sake of simplicity. It is known to provide rotor blades for a gas turbine with such an inner space or cavity connected to a source of a cooling fluid and forming a passage for said fluid. Such gas turbine blades are disclosed in U.S. Pat. No. 3,854,842 and U.S. Pat. No. 4,193,738.
However, such cooling passages of known blades may only provide rather low cooling air velocities due to the limited air mass flow and the difficulty to produce a cavity having a small thickness. Because of the low cooling air velocity only a reduced cooling effect is possible.
In order to improve the cooling effect, GB-A-1 410 014 proposes the provision of a first set of ribs extending in parallel to each other on a first wall of the inner space of the blade and a second set of ribs extending in parallel to each other on a second opposing wall of the inner space of the blade. The ribs are inclined with respect to the rotational axis of the rotor and arranged in such a manner that the first set of ribs crosses the second set of ribs. By such a solution, it is possible to significantly reduce the flow area of the cooling passages without decreasing the thickness of the inner cavity of the blade.
However, this known solution has a substantial deficiency. In a normal rotor blade, the flow area of the cooling passages in the inlet area, i.e. the leading or middle part of the blade, are significantly greater the flow area of the cooling passages in the outlet area, i.e. in the trailing part of the blade, since the thickness of the inner cavity is greater in the central part of the blade or vane than in the trailing end forming the outlet of the cooling passages. This means that the cooling air velocity is lower in the leading and middle parts of the blade than in the trailing part of the blade, i.e. the cooling effect in the leading and middle parts is insufficient.
The object of the present invention is to overcome the above mentioned deficiency and to improve the cooling effect of a rotor blade or a stator guide vane of a gas turbine or any similar rotary machine.
This object is obtained by the component initially defined and characterized in that said first ribs extend in a first direction forming a first angle of inclination to said axis in said leading part and in a second direction forming a second angle of inclination to said axis in said trailing part, and that the first angle is greater than the second angle. By increasing the inclination of the ribs, and thus the cooling fluid channels in the leading area of the channels, the flow area of the channels is significantly reduced, i.e. the velocity and the heat transfer is raised and thus a more effective cooling of the blade or vane is obtained. Such an improved cooling efficiency, which in accordance with the present invention is achieved by a relatively simple measure, increases the lifetime and the reliability of the blade or vane. Furthermore, it is to be noted that a great angle of inclination of the ribs in the leading and middle part of a rotor blade or stator guide vane, increases the stiffness and thus the strength and reliability of the blade or vane.
According to an embodiment of the invention, second ribs project form said second wall and extend essentially in parallel to each other to form second channels for said fluid from said leading inlet part to said trailing outlet part, wherein said second ribs extend in a third direction forming a third angle of inclination to said axis in said leading part and in a fourth direction forming a fourth angle of inclination to said axis in said trailing part, and that the third angle is greater than the fourth angle. By such a channel arrangement, the cooling fluid may be uniformly distributed in the blade or vane, thereby ensuring sufficient cooling of all parts of the blade or vane. Thereby, the directions of the first ribs may intersect with the directions of the second ribs, i.e. for instance the first ribs will slope upwardly from the leading part whereas the second ribs then will slope downwardly from the leading part. By such an arrangement, the second ribs will promote turbulences in the first channels and the first ribs will promote turbulences in the second channels.
According to a further embodiment of the invention, the first ribs are joined to the second ribs in said point of intersection. In such manner, the strength of the blade or vane is significantly improved in comparison with a continuous inner cavity.
According to a further embodiment of the invention, the absolute values of said first and third angles are essentially equal at least in a point of intersection. Moreover, the absolute values of said second and fourth angles may also be essentially equal at least in a point of intersection.
According to a further embodiment of the invention, the first ribs are provided on a suction side of the component and sloping upwardly from said axis and from the inlet part of the channels, and the second ribs are provided on a pressure side of the component and sloping downwardly to said axis and from the inlet part of the channels. By such an arrangement, the air flow heat transfer intensification will be greater on the pressure side of a rotor blade, which increases the cooling effect of the pressure side having a higher temperature than the suction side of the rotor blade.
According to a further embodiment of the invention, said ribs are divided into a leading set of ribs and a trailing set of ribs by means of a gap. By such a gap, a more uniform distribution of the cooling flow may be obtained. Thereby, a projecting element may be provided in at least one of said channels and arranged to increase the turbulence of the cooling fluid, and thus to improve the cooling efficiency. Furthermore, said projecting element may be provided at the inlet zone of at least one of the leading and trailing sets of ribs. The projecting element may be shaped as a rib element, which may project form one of said first and second walls and extend in a direction parallel to an inlet edge line of the actual set of ribs.
According to a further embodiment of the invention, the first angle of inclination is between 40 and 80xc2x0, preferably between 60 and 80xc2x0, and the second angle of inclination is between 10 and 50xc2x0.